Field of the Invention
The present invention relates to a gas sampling device and to a tank filling station comprising such a device.
Related Art
The impurities contained in hydrogen may adversely affect the operation of proton exchange membrane fuel cells (PEMFC) fitted to vehicles and other mobile applications. In order to optimize the performance and life thereof, the hydrogen supplied to the fuel cells needs to meet strict quality requirements which are published in international standards.
Most hydrogen is generally produced via industrial processes such as the steam reforming of natural gas (which is the most commonly used) or the gasification of coal. Hydrogen may also be produced by less conventional processes such as the gasification of biomass or the electrolysis of water.
Purification processes make it possible to generate hydrogen of very high purity (superior to 99.9% depending on circumstances) which may nevertheless still contain impurities the nature and concentration of which are directly dependent on the production process and also the production source (natural gas, coal, naphtha, biomass, water, etc.). Certain impurities (carbon monoxide CO, hydrogen sulfide H2S, ammonia NH3) have an irreversible, or reversible as the case may be, effect on the operation of proton exchange membrane fuel cells. Other impurities (carbon dioxide, oxygen, hydrocarbons, formaldehyde, etc.) have less of an effect on the operation of fuel cells.
All of the impurities are listed in standard ISO 14687-2 which defines the nature and concentration of the species that are to be analyzed.
In order to check the quality of the hydrogen using laboratory analysis techniques, samples of hydrogen need to be taken at the point of use, namely at the high-pressure (350 bar or 700 bar for example) gas outlet of the filling stations.
Most impurities are relatively difficult to analyze. The very low level of concentration desired (for example of the order of one ppb in the case of H2S and around 200 ppb in the case of CO) and the reactivity of certain species (H2S, NH3) with respect to certain materials call for a particularly demanding sampling technique.
The technical constraints associated with such analysis are numerous, and notably:                the gas pressures and flow rates to be analyzed are high,        there is a need to perform chemical passivation of the materials in order to limit the adsorption of contaminants,        the equipment needs to exhibit a high degree of purity,        the hardware used needs to be suited to the high pressure,        the equipment needs to meet safety constraints (“ATEX” explosive atmosphere regulation) etc.        
The ability to take a representative hydrogen sample without the risk of introducing a contaminant, even at a very low content (ppb=parts per billion), is therefore key because it needs to make it possible to evaluate the quality of the fuel supplied to the tanks being filled.
There is an ASTM standard regarding the sampling of hydrogen.
Document CN101418908A1 describes a hydrogen tank filling station incorporating a sampling device. The filling station comprises an outlet connector dedicated to the sampling and sampling gas upstream of the regulating members that regulate the flow supplied to the tank that is to be filled.
Such a device allows a gas sample to be taken at the same time as filling is being carried out but does not guarantee that the hydrogen sampled is under the conditions under which a vehicle is filled. In addition, this device entails the use of components compatible with a relatively high pressure and may be incompatible with the objective of purity of the gas.
This sampling principle also requires relatively complex or costly arrangements regarding the architecture of the filling station.